Stronger measures are needed to to curtail the influence of tobacco companies on Formula One racing, researchers said on Friday, two days before the British Grand Prix.

Tobacco companies are relying more and more on sponsorship of motor sports to promote their products as more direct forms of marketing are being curtailed, they added.

"Formula One has abandoned its commitments to be free of tobacco sponsorship in 2006 and is establishing races in countries with fewer advertising regulations," said Richard Hurt, director of the Nicotine Dependence Center at the Mayo Clinic in the United States.

The report of Hurt and his colleagues is published in the British Medical Journal.

In 1999, British American Tobacco Plc established its own racing team, British American Racing. The researchers said newly produced internal documents show the team has been successful in promoting the company's products.

"Documents also show that BAT was able to develop the global appeal of its brands through extensive broadcast media coverage specifically directed at young people, merchandising proposals and activities aimed at children ... and race sponsorships in emerging markets in Asia," the researchers added.

They urged countries to ratify the World Health Organisation's Framework Convention on Tobacco Control to stop Formula One racing from promoting tobacco products.

"Tougher worldwide action is needed to counter the tobacco industry's influence," they added.